JPH0789537B2 - X-ray reduction projection exposure system - Google Patents

Description

TECHNICAL FIELD The present invention relates to an X-ray reduction projection exposure apparatus for forming a fine pattern on a wafer by using a light source in the vacuum ultraviolet region from X-rays.

[Conventional technology]

As a conventional fine pattern forming method, an exposure method using ultraviolet rays having a wavelength of about 400 nm has been used. However, when the pattern dimension is about 1 μm, the physical resolution limit is reached due to diffraction and interference, and the pattern size is less than 1 μm. It is not useful as a pattern forming method. Shortening the wavelength is considered as a measure for improving the resolution, but in this case, there is no lens material having an appropriate refractive index. A fine pattern can be easily formed by using an electron beam, but there is still a problem in productivity.

Therefore, a method of manufacturing a mask by electron beam exposure and transferring the mask onto the wafer is desired. As a method of this, a method using soft X-rays (0.4 to 4 nm) was proposed in 1972 by Smith et al. In this method, as shown in FIG. 7, a mask 2 having a pattern for absorbing X-rays formed on a film transparent to X-rays and a resist-coated wafer 3 having a thickness of several tens of μm. The patterns on the mask 2 are formed on the wafer 3 by irradiating X-rays 1 from a direction perpendicular to the surface of the mask 2 by arranging them in parallel at intervals.
It is what is transcribed on. It has been confirmed that this method is an excellent transfer technology with features such as high resolution and dust resistance, but for equal-magnification projection, X-ray transfer exceeds the performance of an electron beam exposure machine. Performance (performance such as resolution and alignment accuracy) cannot be improved. In addition, since the exposure is proximity exposure, the minimum pattern size d that can be transferred is d.
Is defined as d = K (Sλ) ^1/2, where S is the gap between the mask 2 and the wafer 3, λ is the wavelength of the light source used, and K is the proportional constant. The gap S is defined by the mask 2 and the wafer 3, respectively. Since there is a limit to the flatness, the minimum pattern dimension d cannot be made smaller than a certain value, and the minimum pattern dimension d cannot be made smaller than a certain value.

When divergent light is used as the light source, a lateral positional deviation Δb called a runout error occurs as shown in FIG. FIG. 8 shows a case where the gap of the mask 2a is larger than the gap S of the mask 2 by ΔS because of large warpage and the like. Here, if the distance between the light source 1a and the mask 2 is D, the target exposure area radius is R, and the gap variation amount from the mask 2 to the mask 2a is ΔS, then Δb = (R / D) ΔS , Δb increases in proportion to the gap variation amount ΔS. Therefore, in order to obtain a highly accurate pattern by proximity exposure, in addition to the position detection mechanism that detects the relative position between the mask 2 and the wafer 3, a mechanism that controls the gap between the mask 2 and the wafer 3 with high accuracy is required. As a result, the device configuration is required to be complicated and sophisticated.

On the other hand, as shown in FIG. 9, as a reduced projection method in the X-ray region, a method using total internal reflection (Proceedings of the 60th Spring Applied Physics Society of Japan p309, pattern using X-ray reflection exposure Transcription, written by Hiroshima University Matsumura). That is, when a parallel light flux is incident on the mask 2 obtained by forming the pattern of the Au (gold) absorber on the Si wafer at an incident angle such that total reflection occurs, a reflected light flux corresponding to the pattern is obtained, If the wafer 3 is placed perpendicular to the reflected light flux, a pattern with a reduction ratio equal to the sine value of the incident angle is obtained. In addition,
Reference numeral 4 in FIG. 9 is a mirror.

In this method, since the total reflection angle in the X-ray region is as small as 1 to 2 degrees or less, the reduction ratio can be extremely large, but conversely, the transfer mask 2 needs to have a large area. Further, in this system, since there is no image forming effect between the mask 2 and the wafer 3, there is a defect that when the distance between the mask 2 and the wafer 3 is increased, the pattern is blurred due to the influence of diffraction. In addition, this method results in a one-dimensional or linear reduction, but not a two-dimensional or planar reduction.

[Problems to be solved by the invention]

As described above, in the conventional apparatus, the resolution in proximity exposure is low, and it is difficult to create a mask to increase the resolution at the same size. 6 axes (three directions and three rotation angles with respect to these axes) are required to be aligned with high accuracy, and there is a problem that it is difficult to judge pass / fail of a mask pattern having a fine structure.

[Means for solving problems]

In order to solve such a problem, according to the present invention, a first substrate having a figure arranged at a position apart from an optical axis of a reduction optical system, which will be described later, and X-rays are incident on the first substrate. An incident means, a second substrate having photosensitivity to X-rays, X
A reduction optical system which is located between the first substrate and the first substrate along the traveling direction of the line and which makes X-rays from the first substrate enter at a position separated from the optical axis by a predetermined distance. A light-shielding plate that is located between the reduction optical system and the light source and has an arcuate cutout that is concentric with the axis of the reduction optical system; and a first substrate and a second light-shielding plate for the light-shielding plate. The apparatus is provided with a moving unit that moves the substrate in synchronization.

[Action]

In the present invention, the pattern on the mask is reduced and projected onto the wafer, and the mechanism for holding the mask and the mechanism for holding the wafer move in synchronization.

〔Example〕

The resolution of the image point in the Franhoffer diffraction of the reduction optical system is
If the wavelength of the light source is λ and the numerical aperture of the optical system is NA, then ε = 0.
It can be considered from the relationship of 5 × λ / NA. Now, assuming that the resolution on the image plane is 0.1 μm and the wavelength λ = 100Å, the NA is 0.05. In the design of the reduction optical system in the X-ray region, since the wavelength λ is small, the NA can be reduced by one digit or more as compared with the NA with ultraviolet light having the same resolution.

Next, the depth of focus fd is given by fd = ± λ / (2NA ² ). As NA decreases, fd increases,
Increase the depth of focus margin. For example, NA = 0 in the above example.
05, and at λ = 100Å, fd = ± 2μm. This value is larger than the depth of focus when the same resolution is obtained with an ordinary optical system, which is advantageous in device configuration.

The wavelength λ can be determined from the viewpoint of the reflectance of the multilayer mirror used. That is, the reflectance R of the multilayer mirror is the wavelength λ
The number of layers N must be proportional to 1 / λ ² in order to obtain a certain reflectance in proportion to the fourth power of 4 A rate of film is obtained.
Further, when a reflective optical system is configured with a plurality of multilayer film mirrors, it is necessary that the peaks of the spectral reflectance wavelengths overlap between the plurality of multilayer film mirrors, and λ / Δλ is small, that is, The wider the band width, the better, but λ
/ Δλ is proportional to the square of the number of layers. Therefore, in the reduction optical system, the longer the set wavelength is, the more advantageous it is. The relationship between the surface roughness and the reflectance of the multilayer mirror is given by R = exp (-2 (2πσCOSα / λ) ² ). Here, α is the incident angle, σ is the surface roughness, and it can be seen that the influence of the surface roughness decreases as λ increases.

Furthermore, when continuous wavelengths such as synchrotron radiation are used, wavelength components other than the design wavelength λ of the multilayer film need to be cut because they adversely affect image formation, but X-ray absorption increases as the wavelength becomes longer. Becomes large, and it becomes difficult to cut out only the design wavelength. There are Al, Mg, Si, SC as filter materials with good transmittance in the wavelength band of 40 Å or more,
It is advantageous to set a wavelength band longer than the absorption edge, that is, a wavelength band of 40 Å to 400 Å.

FIG. 1 is a block diagram showing the first embodiment of the present invention. First
In the figure, 3 is a wafer as a second substrate coated with a resist, 5 is an X-ray, 6 is a mask as a first substrate for generating contrast against X-rays, and 7 is a concave mirror as a reduction optical system. Is. The X-rays incident on the mask 6 from the incident means (not shown) become a reflected light flux according to the absorption pattern formed on the mask 6 and are two-dimensionally reduced by the concave mirror 7, and then on the wafer 3 coated with the resist. Image on. That is, in the figure, the point A0 on the mask 2 is imaged at the point A1 on the wafer 3, and the point B0 is imaged at the point B1. The optical system as shown in FIG. 1 has alignment means (not shown) for aligning the wafer 3 with respect to the mask 6 in order to accurately form the image of the mask 6 on the wafer 3.

In FIG. 1, when the concave mirror 7 is a multilayer mirror in which thin films of heavy elements and light elements are alternately formed,
An image forming system with almost vertical incidence can be formed, and the mask 6 and the wafer 3 can be arranged on the axis L of the concave mirror 7 or in the vicinity thereof, so that an image forming optical system with small aberration can be formed. Here, it is possible to use a transmission type as the mask 6 when the wavelength λ is 50 Å, but X-ray absorption increases as the wavelength becomes longer, and there is no suitable transmission material. Inevitably, the stencil mask will consist of only the body, and it will be difficult to create with a slightly complicated LSI pattern. On the other hand, a reflective mask having a light element as an absorption layer and a heavy element having a high X-ray amplitude reflectance as a reflecting surface, that is, a desired pattern is easy to manufacture.
It is easy to obtain pattern contrast for lines and can be used in a wide wavelength range.

FIG. 2 is a block diagram showing the second embodiment of the present invention. In FIG. 2, reference numeral 7 is a concave mirror having a multilayer film formed thereon, 8 is a light shielding plate having an arcuate cutout 8a, 9 is a total reflection type reflection mirror having a curvature, 10 is a mask holding and aligning mechanism, and 11 is a wafer. It is a holding and aligning mechanism.

In FIG. 2, light incident parallel to the optical axis L of the spherical mirror and close to the axis crosses the axis having a radius of curvature 1/2 of the spherical surface, but as it deviates from the axis, Due to the aberration, the intersection point on the axis moves, and the pattern at the image forming point becomes blurred. However, the light passing through a position at a height higher than the axis and the light passing through the vicinity of the position have a smaller variation in the intersection with the axis after reflection as the width at that position becomes narrower, that is, the pattern blurring at the image forming point. Can be made smaller. Therefore, a light-shielding plate 8 having a narrow arc-shaped cutout is placed at this position, and other components are cut, so that an imaging pattern with a small blur can be obtained. As described in the beginning of this [Embodiment] section, the NA required for obtaining fine resolution in the X-ray region may be small because the wavelength is short, and only a part of one concave mirror is required. By using, it is possible to form a pattern without aberration. For example, a reduction ratio of 1/10 and a wavelength of 10
In the example of the resolution ε = 0.1 μm on the 0Å image plane, the numerical aperture NA on the mask surface is NA = 0.005, and if the distance between the notch and the object is 100 mm, the notch may be 0.5 mm. Since the image forming pattern at this time is a cutout 8a on the circular arc of the light shielding plate 8 reduced, in order to obtain an exposure pattern of a large area, a moving means (not shown) is used.
The holding and aligning mechanisms 10 and 11 are synchronized with the light shielding plate 8 which is fixed concentrically with the axis of the reduction optical system and the wafer holding and aligning mechanism 11 is provided.
It is possible to form a pattern of a wide area on the mask 6 on the wafer 3 by moving at a low speed relative to the mask holding and aligning mechanism 10 by the reduction ratio.

The incident light is incident on the reflection mirror 9 at an angle such that total reflection occurs. The reflection mirror 9 is provided to improve the mirror incidence efficiency when the incident light 5 is the synchrotron radiation light, and collects the rectangular synchrotron radiation light in an arc shape, and wavelength selectivity according to the incident angle. It is something that has. As the reflection mirror 9, a diffraction grating or a multilayer film mirror can be used instead of the total reflection mirror. Although the mask 6 is a reflective type, the same effect can be obtained by using a transmissive type.

FIG. 3 is a constitutional view showing a third embodiment of the present invention, in which a convex mirror 12 is added to the concave mirror 7 of FIG. 2 in order to make the formed pattern smaller in aberration. . In FIG. 3, the concave mirror 7 and the convex mirror 12
Constitutes a reduction optical system.

FIG. 4 shows a fourth embodiment of the present invention in which the mask 13 is of a transmission type.

In FIGS. 3 and 4, the X-ray reflected or transmitted by the mask 6 or 13 is the convex mirror 12 having a multilayer film formed thereon.
Concave mirror 7 that is magnified and reflected by a multilayer film
The light is focused by and the pattern on the mask 6 or 13 is imaged on the surface of the wafer 3. As in the case of FIG. 2, since the pattern on the wafer 3 is an arc-shaped pattern by the light shielding plate 8, the holding and aligning mechanisms 10 and 11 are moved in synchronization with the light shielding plate 8 to make the pattern wider. The pattern on the mask of area can be exposed on the wafer. 2 in this case
The radius of curvature ratio of the two mirrors is optimized for minimum aberration by a method such as ray tracing. By setting the value of the radius of curvature ratio to be in the range of 2.4 to 2.6, optimum configuration conditions can be obtained and a pattern with small aberration can be formed. .

FIG. 5 is an example of the calculation result of spherical aberration in two mirrors, in which the horizontal axis shows the amount of aberration, the vertical axis shows the distance from the optical axis (axial height), and the radius of curvature of the concave surface with respect to the radius of curvature of the convex surface. Is shown as a parameter. A condition with a small change in aberration can be found near the axial height of 11 mm when the radius ratio is 2.4, and near the axial height of 8 mm when the radius ratio is 2.5.By constructing an optical system that passes only in this vicinity, a good result can be obtained. An image pattern is obtained.

In the example of FIG. 5, the radius of the convex spherical surface is 20 mm,
The same applies to other cases as shown in FIG. Figure 6 shows
The results are obtained when the radius of the convex spherical surface is changed from 10 mm to 100 mm.

〔The invention's effect〕

As described above, the present invention installs the reduction optical system between the first substrate and the second substrate along the X-ray traveling direction,
By arranging the first substrate at a position away from the optical axis of the reduction optical system, reduction projection exposure in the vacuum ultraviolet region from X-rays can be configured, so that exposure in a large area becomes possible and 1 μm or less. A fine pattern can be easily obtained, and the pattern size on the mask can be a reticle pattern that is 5 to 10 times larger, facilitating production, and using the conventional equipment for mask inspection and repair technology. There is an effect that a manufacturing process of a certain degree can be used.

In addition, the reduced projection exposure configuration has an effect of increasing the alignment margin between the mask and the wafer, and eliminating the need for strict mechanical precision in proximity exposure.

Furthermore, by placing a light-shielding plate having a cutout concentric with the optical axis of the reduction optical system and synchronizing the mask and the wafer,
A large number of aberration-free patterns can be reduced and transferred onto a wide area of a wafer, and a narrow visual field size, which is a problem in a refracting optical system of 25000Å or less, can be solved.

[Brief description of drawings]

1 to 4 are configuration diagrams showing first to fourth embodiments of an X-ray reduction projection exposure apparatus apparatus according to the present invention, FIGS.
FIG. 7 is a graph showing the calculation result of spherical aberration, FIG. 7 is a configuration diagram for explaining a conventional fine pattern forming method, FIG. 8 is an explanatory diagram showing runout error, and FIG. 9 is a conventional total reflection type. It is a block diagram which shows an X-ray reduction projection exposure apparatus. 3 ... Wafer, 5 ... Incident light, 6,13 ... Mask, 7 ...
Concave mirror, 8 ... Shading plate, 8a ... Notch, 9 ... Reflective mirror, 10 ... Mask holding and aligning mechanism, 11 ... Wafer holding and aligning mechanism, 12 ... Convex mirror.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nao Ishihara 3-1, Morinosato Wakamiya, Atsugi City, Kanagawa Pref., Atsugi Telecommunications Research Laboratories, Nippon Telegraph and Telephone Corporation (56) Reference JP-A-62-9632 (JP, A)

Claims (2)

[Claims] 1. A first substrate having a figure, an incidence means for injecting X-rays on the first substrate, a second substrate having photosensitivity to X-rays, and a traveling direction of X-rays. A reduction optical system positioned along the first substrate and the first substrate, and a circle positioned between the reduction optical system and the light source and concentric with the axis of the reduction optical system. A light-shielding plate having an arcuate notch and a moving unit that moves the first substrate and the second substrate in synchronization with the light-shielding plate are provided, and the first substrate is the light of the reduction optical system. The X-rays are arranged at a position apart from the axis, and the X-rays from the first substrate are made to enter at a position apart from the optical axis of the reduction optical system by a predetermined distance. Reduction projection exposure apparatus. 2. The reduction optical system is composed of concave and convex spherical mirrors, and the ratio of the radius of curvature of the concave spherical mirror to the radius of curvature of the convex spherical mirror is 2.4 to 2.6. 2. An X-ray reduction projection exposure apparatus according to claim 1.